Extreme Ultraviolet Tool Research Articles

Evaluation of Lines and Spaces printing and general understanding of imaging with dark field low-n mask

BackgroundOne of the ways to push down resolution limits in extreme ultraviolet (EUV) lithography is to use alternative masks. New types of absorbers are being broadly investigated for current 0.33 NA as well as for high NA of 0.55.AimWe study the imaging performance of a low-n/low-k absorber (ABS) dark field (DF) mask for lines and spaces (LS) printing at 0.33 NA.ApproachExperimentally and via simulations, we investigate the use of low-n DF masks for a metal direct print application and compare low-n mask performance with Ta-based ABS masks.ResultsCompared to a Ta-based ABS mask used nowadays, the low-n DF mask brings contrast gain for dense LS. Also, for low-n masks, we observe large best focus (BF) shifts for isolated features with respect to dense features and change of bias. Hence, strong mask critical dimensions (CD) control is needed. We demonstrate how adding assist features can align BF through pitch. In addition, placing subresolution assist features (SRAFs) significantly enhances exposure latitude for semi/iso and iso-LS and improves the overlapping process window for selected cases.ConclusionsThese investigations show that low-n DF masks can enhance the imaging of LS through pitch if SRAFs are used and a good mask CD control is achieved. Our work further adds fundamental understanding to advantages observed for a metal direct print application of alternative ABS masks for the current and future EUV tools.

Study of a linear surface wave plasma source for tin removal in an extreme ultraviolet source

Tin deposition mitigation employs hydrogen radicals and ions, formed in a hydrogen plasma, to interact with tin to form tin hydride (SnH4) in the gaseous state, which is then pumped away. Surface wave plasma (SWP) technology developed at Illinois generates hydrogen radicals and ions, resulting in tin etch rates that are high enough to keep extreme ultraviolet (EUV) lithographic tools clean. An advantage of an SWP antenna is the ability to generate a high density of hydrogen radicals and hydrogen ions directly at the desired etching location. In situ etching of tin enables high availability EUV tools by maintaining high reflectivity of the multilayer mirror of the collector. Additionally, the SWP is characterized with low ion energies and low electron temperature, such that the multilayer mirror does not suffer any damage from sputtering or implantation of hydrogen ions during operation. Here, experiments elucidating the fundamental processes of tin removal are conducted by varying pressure, power, surface temperature, and gas flow rate in order to observe the etch rate behavior. Our results have shown that the presence of hydrogen ions increases etch rates because ion bombardment weakens Sn–Sn bonds, which, in turn, allows for a higher rate of chemical etching by the radicals. The ion bombardment reduces the number of radicals needed to etch a single tin atom to the range of 102–103. The linear SWP antenna yields plasma densities on the order of 1017to1018m−3 and radical densities on the order of 1018to1019m−3, allowing for greater utilization of ion etch enhancement. Etch rates of up to 200 nm/min have been achieved. The surface temperature of the samples is an important factor in the etching process such that the decrease in the surface temperature increases the etch rates and decreases the hydrogen desorption rates. In addition, a kinetic etch model is developed to explain the behavior of etch rates as a function of surface temperature. Furthermore, results from experiments performed in an Illinois NXE:3100 chamber will be discussed.

ITRS lithography roadmap: 2015 challenges

Abstract In the past few years, novel methods of patterning have made considerable progress. In 2011, extreme ultraviolet (EUV) lithography was the front runner to succeed optical lithography. However, although EUV tools for pilot production capability have been installed, its high volume manufacturing (HVM) readiness continues to be gated by productivity and availability improvements taking longer than expected. In the same time frame, alternative and/or complementary technologies to EUV have made progress. Directed self-assembly (DSA) has demonstrated improved defectivity and progress in integration with design and pattern process flows. Nanoimprint improved performance considerably and is pilot production capable for memory products. Maskless lithography has made progress in tool development and could have an α tool ready in the late 2015 or early 2016. But they all have to compete with multiple patterning. Quadruple patterning is already demonstrated and can pattern lines and spaces down to close to 10-nm half pitch. The other techniques have to do something better than quadruple patterning does to be chosen for implementation. DSA and NIL promise a lower cost. EUV promises a simpler and shorter process and the creation of 2-D patterns more easily with much reduced complexity compared to multiple patterning. Maskless lithography promises to make chip personalization easy and to be particularly cost effective for low-volume chip designs. Decision dates for all of the technologies are this year or next year.

Cleaning of Organic Contamination from EUV Optics Surfaces Using Hydrogen-based Plasmas

The efficiency of optics used in extreme ultraviolet (EUV) range suffers from reflectivity degradation due to oxidation and carbon contamination of mirror surfaces. Therefore, an efficient cleaning procedure should be ascertained in order to facilitate applications of EUV lithography tools. Carbon contamination removal from the mirror surface has been reported in Hydrogen plasmas, and laser-induced Hydrogen plasmas in EUV tools. Here, we performed measurements in a helicon-type RF plasma reactor with hydrogen pressures similar to the ones used in laser-induced plasmas in EUV tools. The method of optical actinometry was used to determine hydrogen atom concentration and the degree of dissociation. The results are compared to those obtained by pressure-rise measurements. Preliminary results of plasma etching of thin organic films (PMMA) were also obtained to assess the cleaning efficiency.

Materials challenges for sub-20-nm lithography

We discuss the future of resist materials for sub-20-nm lithography and believe that polymer-bound PAG-based resists will be used to 16-nm node. There has been enough progress in resolution and sensitivity to justify the use of these materials. Polymer-bound PAG resists have shown that the principal demerit of acid diffusion can be overcome through attachment of the PAG anion to the lithographic polymer. Since the introduction of this chemically amplified resist approach, we have seen steady improvement in resolution, sensitivity, and LWR. We have also seen improvement in OOB response, outgassing, and pattern collapse. There is no doubt that continuous improvement is still required for these resist systems. We believe that increasing the overall resist quantum yield for acid generation substantially improves the shot-noise problem thereby leading to faster high-resolution resist materials. Using a 0.30-NA extreme ultraviolet tool with dipole, we can achieve 22-nm hp resolution, with a 12-mJ dose and a 4.2-nm LWR.

Actinic inspection of extreme ultraviolet programed multilayer defects and cross-comparison measurements

The production of defect-free mask blanks remains a key challenge for extreme ultraviolet (EUV) lithography. Integral to this effort is the development and characterization of mask inspection tools that are sensitive enough to detect critical defects with high confidence. Using a single programed-defect mask with a range of buried bump-type defects, the authors report a comparison of measurements made in four different mask inspection tools: one commercial tool using 488nm wavelength illumination, one prototype tool that uses 266nm illumination, and two noncommercial EUV “actinic” inspection tools. The EUV tools include a dark field imaging microscope and a scanning microscope. Their measurements show improving sensitivity with the shorter wavelength non-EUV tool, down to 33nm spherical-equivalent-volume diameter, for defects of this type. Measurements conditions were unique to each tool, with the EUV tools operating at a much slower inspection rate. Several defects observed with EUV inspection were below the detection threshold of the non-EUV tools.

Silicon Containing Organic-Inorganic Hybrid Materials as EUV Photoresists

The opportunities posed by extreme ultraviolet (EUV) lithography are encouraging the development of new resist platforms. The absorbance characteristic of materials required for the EUV lithography demands the use of polymers containing highly transparent silicon atoms. At the same time, very low levels of outgassing of silicon containing fragments are required due to the vacuum environment present during exposure and the extremely high cost of the EUV tools. These two contradictory requirements have led us to pursue new types of silicon containing hybrid materials as a resist platform; chemically amplifiable polysilanes and silsesquiazanes. In the former case, the direct incorporation of acid sensitive groups into the polymer backbone allows for a solubility switch upon exposure. In the later system, a silicon-nitrogen backbone structure can be cleaved upon exposure to induce a solubility switch. These hybrid materials possess many useful properties including low absorbance, low outgassing, and high sensitivity. Silsesquiazanes having different substituents and branching ratios were synthesized. The properties of the polymers will be discussed in the context of their lithographic performance.